Somehow, the fighters on the 13th season of "The Ultimate Fighter" managed to crack Brock Lesnar's sometimes-cold exterior.

The former champ didn't have much of a choice, anyway. He was all-in once he accepted the job as a head coach.

But Lesnar also surprised himself in how emotionally involved he got when his team fought with Junior Dos Santos' squad during the filming of the reality show, which debuts Wednesday on Spike TV.

"When you're forced to be around people … I wanted the best for the guys," Lesnar told MMAjunkie.com (www.mmajunkie.com) of his experience coaching "TUF 13." "I just found myself getting invested for them guys to win and be successful."

"The Ultimate Fighter 13" features 14 welterweights who complete in single-elimination tournament for a six-figure UFC contract.

It may not have been Lesnar's first plan to get invested when he arrived on set. He had his own reasons for taking the coaching job: a plush setup in Las Vegas for his family, a nice check from the UFC and Spike TV, and most importantly, a chance to even the score with the man who took his belt, Cain Velasquez.

Overall, he said, the positives outweighed the negatives, so he took the gig. But somewhere along the way, he got drawn into the coaching process. He found himself going far beyond what he'd normally do with someone outside his circle, which is probably not much.

"There's a point in the show where we put in a lot of time with a certain individual, and there's some success that builds into it," Lesnar said. "So yeah, you get attached in some ways.